The task of removing chemicals from aqueous solution, especially when they are present at low concentration, has been a commercial engineering problem for many years. This has been one of the main problems in making biotechnology commercially effective for a wide array of products. These problems commonly contribute to the high cost of remediating water contaminated with toxic materials or materials that could be recycled and reused if collected from the water.
In a chemical process, the separation and purification of the desired chemical in the aqueous phase can easily reach 40% of the cost of the chemical production even after all filterable solids are removed from the solution. The cost is higher the lower the concentration of produced chemical. In the process of removing a contaminant from water, it can be the bulk of the cost.
Conventionally, resin beds using absorbent resins are frequently used for chemical separations. In this technology, the highly filtered aqueous solution is pushed under pressure through a bed of resin wherein the resin adsorbs the chemical. The chemical is then washed off the bed by another solution in a more concentrated form. The flow through the bed must be uniform and precise and the system requires considerable hydraulic pressure. The resin beads are usually on the order of 100 micrometers or so and do not have the high surface area of a colloidal particle bead or nanoparticle bead. If the particles are made too small, the pressures needed may be excessive.
In the case of remediation technology, expensive resins are not usually the choice. Activated carbon filters commonly are used and the carbon with contaminant is collected and subsequently burned in hazardous waste incinerators.
The use of nanoparticles for the adsorption of chemicals has been proposed for many years. Although recently renamed “nanotechnology”, small particle chemistry has been known from the mid 19th century and in the 20th century these types of particle were included in the class of physical state covered by the discipline known as “colloid chemistry” or “colloid science”. By either name, a common difficulty has always been the manipulation of particles that are difficult to handle, difficult to see and collect, and potentially hazardous in their dry and dusty state. See, e.g., “Separation and purification techniques in biotechnology” by Frederick J. Dechow, Reed & Carnrick Pharmaceuticals, Piscatawy, N.J., Noyes Publications, Park Ridge, N.J., 1989; “Biochemical Engineering” by James M. Lee, Washington State University, Prentice hall, Englewood Cliffs, N.J., 1992; and “Separation, Recovery, and Purification in Biotechnology Recent Advances and Mathematical Modeling” by Juan A. Asenjo, EDITOR Columbia University, Juan Hong, EDITOR, Institute of Technology, Developed from a symposium sponsored by the Division of Microbial and Biochemical Technology at the 190th Meeting of the American Chemical Society, Chicago, Ill., Sep. 8-13, 1985, American Chemical Society, Washington, D.C. 1986, the entire contents of which are incorporated herein by reference in the entirety.
The higher surface area of such particles makes them a great candidate for improved separation and purification processes; however, their use has been extremely limited to date.
Reduction of Contaminants
In reclamation efforts it is often necessary to reduce the levels of contaminants in liquids for any number of reasons, including meeting discharge standards or preparing the liquid for reuse. It can be particularly costly to reduce concentrations of chlorinated hydrocarbons, metals and certain other contaminants.
Air stripping, for instance, is a previously disclosed method for treating chlorinated solvents in water. This process involves blowing air through contaminated water, by which the solvents in the water are rendered airborne. The airborne solvents can then be captured, such as by carbon filters, for later disposal or destruction by proper means. The use of aeration, carbon filters, and the need for disposal make this process time consuming and expensive. The treatment of metal contaminants is currently much more difficult than organic solvents, requiring ion exchange treatment or chemical transformation to forms that can be collected by filtration.
Hydrogenation can be an effective way by which to reduce numerous contaminants, such as chlorinated solvents and metals. Unfortunately, normal hydrogenation using gaseous hydrogen usually takes place at high temperatures (up to 400° C.) and high pressures (up to 5,000 psig or 341 atm). The vessels required for such hydrogenation are expensive and the process is relatively dangerous. However, several decades ago it was found that certain inorganic compounds such as NaBH4, CaH2, KBH4, LiAlH4 (collectively called hydrides) were capable of reducing various compounds by hydrogenation in less severe conditions than that required for hydrogen gas. The disclosed method uses hydrides to reduce the concentration of certain contaminants in liquids.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of one or more of the problems set forth above.